Electronic circuits (“circuits”) may be designed to meet certain desired design criteria. Circuits may be powered by various voltages, and logic circuits may be designed to have logic levels defined at differing voltages. The power supplied to the circuits, and in particular the voltage, may depend on such mundane criteria as what is available to run the circuit. However, many types of electronic circuit's performance may be enhanced by the choice of voltages used in a circuit. Also, ease of integrated circuit fabrication may lead to choices of operating voltages suitable for the fabricated circuit. Circuit types or families may include circuits having common interface characteristics such as operating voltage and logic levels. Circuit families may also have similar construction such as common utilization on MOS transistors, bipolar transistors, or the like.
These design trends have led to the development of various electronic circuit families or types, such as the exemplary circuit families of CMOS, TTL, ECL, and the like. Each of these circuit families may utilize different power supply voltages based on performance, fabrication concerns, or the like. Also, since these circuits may be used to implement digital logic functions, different voltage levels may be used to indicate or represent ones and zeros. In addition, some circuits may be designed to operate utilizing more than two logic levels.
For example, TTL circuits may operate from 5 volt power supplies to implement digital logic circuits. The 5 volt power supply may be useful in generating voltage levels representing ones and zeros that may be useful in switching the bipolar transistors that may make up a TTL circuit on and off. These circuits were very robust and not easily damaged by static electricity, but are not used much any more because once turned off, all memory in the circuit would typically be lost.
Exemplary CMOS circuits may operate from low voltage power supplies and may utilize lower voltages to implement ones and zeros to activate MOS transistors that make up circuits in this family. This family of circuits may retain their memory when turned off, but are fragile and easily damaged by static electricity. There are numerous other examples of differing types of circuits and their suitability in various applications.
A trend in modern circuit design has been the mixed use of various types of circuits, often operating from various voltages and having differing voltages to represent ones and zeros. Mixing circuit families can have the advantage of the beneficial characteristics of these differing circuits available to designers, a challenge may be to increase interoperability and compatibility between the various circuit types. An area of challenge in these designs has been providing an interface busses or connections, and circuitry to satisfactorily translate and transfer logic signals between circuits operating at various voltage levels.